The present invention relates to the mounting of a flat crystal made of hard material, sapphire type for example, at the top of the body of a watch case.
The use of crystals of hard material is becoming increasingly widespread at the present time for fine watchcases, not only because of their excellent abrasion resistance but also because they will permit structures of smaller thickness due to their rigidity.
Accordingly, many methods have already been proposed for mounting such crystals in the opening of a case body or bezel. One is cementing which will not permit ready replacement of the crystal and will not always provide a good seal over space time. Another method is setting the crystal in a recess with interposition of a sealing strip which has the disadvantages of requiring a recess sufficiently high to retain the crystal by friction and extending around the entire perimeter of the body, which limits the ability of making the case out of precious material.
There are also other designs in which a flat crystal of hard material is inserted laterally in tracks provided on opposite sides of the body. It is then possible to make cases of very special styling in which the crystal extends to the edge of the body on its other two sides, but the engagement of the crystal in the tracks may cause damage to the sealing strip. In addition, the requirement of tracks limits the possible shapes of the case.
Accordingly, the invention comprises a watch case fitted with a flat crystal of hard material, in which the means of mounting the crystal on the body, or possibly in a bezel, do not have the above-mentioned disadvantages, and the crystal may be readily attached and removed without danger of displacing or damaging the seal. The present invention provides new possibilities in terms of shape and styling of the case.
The objects are achieved by providing means to engage the crystal under pressure between the elastically deformable side walls of a recess made in the body, the facing surfaces of said side walls and of the edge of the crystal being inclined relative to the axis of the case.
Of course, the recessed mounting of a crystal on a body is known per se, but not the recessed mounting of a flat crystal of hard material. For example, Swiss patent application No. 17,027/66 or French Pat. No. 1,398,410 and 2,395,536 describe watchcases in which the crystal is provided with an annular skirt or border elastically deformable so as to lock against matching surfaces provided on the edges of the body opening. But this arrangement is limited to a flat, rigid crystal having an annular skirt on the body. One of the important features of this invention is to provide a recess over only a portion of the periphery of the crystal without impairing the seal of the assembly by using the intrinsic elasticity of the material of which the body is made to supplement the rigidity of the crystal and ensure a proper retention of the crystal. The restoring force exerted by the side walls of the recess on the edge of the crystal in conjunction with the rigidity of the crystal does serve to ensure perfect application of the bottom face of the crystal to a sealing strip throughout the perimeter of the latter, even if only locally retained in the recess.